Many different computing applications rely on some type of storage medium for the persistent storage of various kinds of application data. For example, common office applications and multimedia applications generate and use application data of various types and formats, such as documents, spreadsheets, still images, audio and video data, among others. Frequently, such data is stored for repeated access or use on behalf of a user. For example, a user may wish to store and work with a number of documents or other data over a period of time, and may expect that the data will be readily available in a predictable state when needed.
In conventional computing systems, the storage medium used by applications for persistent application data storage is most commonly a magnetic fixed drive or “hard drive,” although optical and solid-state storage devices are also used. Such devices are either integrated within a computer system that executes the applications or accessible to that system via a local peripheral interface or a network. Typically, devices that serve as application storage are managed by an operating system that manages device-level behavior to present a consistent storage interface, such as a file system interface, to various applications needing storage access.
This conventional model of application storage presents several limitations. First, it generally limits the accessibility of application data. For example, if application data is stored on the local hard drive of a particular computer system, it may be inaccessible to applications executing on other systems. Even if the data is stored on a network-accessible device, applications that execute on systems outside the immediate network may not be able to access that device. For example, for security reasons, enterprises commonly restrict access to their local area networks (LANs) such that systems external to the enterprise cannot access systems or resources within the enterprise. Thus, applications that execute on portable devices (e.g., notebook or handheld computers, personal digital assistants, mobile telephony devices, etc.) may experience difficulty accessing data that is persistently associated with fixed systems or networks.
The conventional application storage model also may fail to adequately ensure the reliability of stored data. For example, conventional operating systems typically store one copy of application data on one storage device by default, requiring a user or application to generate and manage its own copies of application data if data redundancy is desired. While individual storage devices or third-party software may provide some degree of redundancy, these features may not be consistently available to applications, as the storage resources available to applications may vary widely across application installations. The operating-system-mediated conventional storage model may also limit the cross-platform accessibility of data. For example, different operating systems may store data for the same application in different, incompatible formats, which may make it difficult for users of applications executing on one platform (e.g., operating system and underlying computer system hardware) to access data stored by applications executing on different platforms.
Some servers include a number of hard disk drives (for example, eight or more hard disk drives) to provide adequate data storage. Typically, the hard disk drives for servers are of a standard, off-the-shelf type. Standard, off-the-shelf hard disk drives are often a cost effective solution for storage needs because such hard disk drives can be obtained at relatively low cost. Nonetheless, in server designs using such standard hard disk drives, the arrangement of the hard disk drives may leave a substantial amount of wasted space in the server chassis. This wasted space, especially when multiplied over many servers in a rack, may result in inadequate computing or storage capacity for a system.
Hard disk drives include motors and electronic components that generate heat. Some or all of this heat must be removed from the hard disk drives to maintain continuous operation of a server. As with other components, hard disk drives fail from time to time while in service. These failures reduce the storage capacity of a system. To restore capacity, servers may need to be powered down and removed from a rack so that the defective hard disk drives can be replaced or repaired.
In some systems, such as archival, backup, or disaster recovery systems, a vast amount of data may need to be stored, though any particular piece of the stored data may be accessed only rarely. Magnetic tape systems are often used to store archival data. Magnetic tape drives, however, may be fragile and susceptible to adverse environmental conditions, such as heat and humidity. In addition, some magnetic tape drives have relatively high failure rates.